Publication Type:

Journal Article

Authors:

Lafrance, Bruno; Bygnes, Lindsay; McDonald, Andrew M.

Source:

Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre, National Research Council of Canada, Ottawa, ON, Canada, Volume 51, Number 5, p.466-484 (2014)

ISBN:

0008-4077

Keywords:

basement, breccia, Canada, chemical composition, dikes, diorites, eastern canada, electron microscopy data, emplacement, igneous rocks, impact breccia, impactites, intrusions, isotope ratios, Isotopes, Lead, metals, Metamorphic rocks, mineral composition, Ontario, Paleoproterozoic, Pb-207/Pb-204, petrography, plutonic rocks, Precambrian, proterozoic, quartz diorites, radioactive isotopes, SEM data, Stable isotopes, Sudbury structure, theoretical models, upper Precambrian, x-ray diffraction data

Abstract:

The Whistle offset dike is a radial dike linked to the ca. 1850 Ma Sudbury Igneous Complex (SIC) in Sudbury, Ontario. It is linked through the funnel-shaped Whistle embayment which formed as a depression along the floor of a superheated impact melt sheet represented by the present-day SIC. The dike consists of metabreccia, quartz diorite, and inclusion-bearing quartz diorite, emplaced in older Archean gneisses and intrusions. Metabreccia has a fine-grained, igneous-textured matrix surrounding Archean basement clasts. It overlaps in major-element compositions (MgO, CaO, SiO (sub 2) ) with the two quartz diorites. The three have similar chondrite-normalized rare-earth element patterns characterized by pronounced negative slopes, i.e., (La/Yb) (sub N) =17-29, and a weak negative Eu anomaly. This suggests that they originated from the same source melts. Metabreccia has higher high-field-strength element (HFSE) ratios, i.e., Gd/Yb, Ce/Yb, Zr/Y, and lower model initial (super 207) Pb/ (super 204) Pb isotopic ratios than the two quartz diorites, suggesting that it assimilated more Archean rocks with higher HFSE ratios and lower (super 207) Pb/ (super 204) Pb ratios. It formed as SIC melts mixed with melted basement rocks at the SIC-basement contact. This produced a strongly contaminated, inclusion-bearing melt, which drained downward into an offset structure or fault, entrained more fragments plucked from the walls of the fault, and crystallized as metabreccia. Less contaminated quartz diorite was then emplaced in the still-viscous metabreccia during reactivation of the fault caused by isostatic readjustment of the gravitationally unstable crater. More melting, assimilation of clasts, and mixing of SIC melts at the SIC-basement contact produced inclusion-bearing quartz dioritic melts that were emplaced last along the Whistle offset fault.

Notes:

GeoRef, Copyright 2018, American Geological Institute.<br/>2015-007608<br/>Whistle Dike